This guide proposes a simple method to conceive your own electrosensitive multi-user surface.. It has a 64 dots (8x8) resolution, easily extensible up to 256 (16x16). It works with a Stamp stack microcontroller. Total cost is around 375.00 CAD and may vary depending on material and size. The interface was designed and built as part of the Travel agent immersive interactive installation project, realized at BEK by the Drone and S.O.U.P. collectives; the work was showcased during the Piksel 05 festival.

Operation is simple: a sweeping is carried out on 8 aluminium strips. Separated by an insulator, 8 other strips collect the points of contact. The information is treated by a microcontrollor and transmitted to a computer.

 

Ingredients

Carpet

  • Paperboard
  • Insulating foam 1.5 cm thick
  • Aluminium (preferably self-adhesive)
  • Flexible carpet (to cover the whole)

Electronics

  • Stamp Stack 2
  • 74hc595
  • 74hc165
  • Flat cable
  • Serial cable (rs-232)

The Surface

Surface is made up of 3 layers.

First, a rigid layer of paperboard which is used both to protect and support 8 horizontaly aligned strips of aluminium.

Second, a layer of insulator (syntetic fibre), perforated in order to let the current pass when compressed. Ideally the holes should be cut exactly at the points of contact.

Finally a last layer of rigid paperboard which is used to support 8 verticaly aligned aluminium strips (with the first layer strips, they thus form an 8 X 8 grid).

Preferably, the whole must be covered with a light carpet (or a thick fabric) in order to protect it from the intensive uses.

The Circuit

I separated the circuit in two parts.

First the microcontroller, which includes the Stamp Stack, the 74hc165 and the 74hc595 (serial-parallel converter). Second, comes the protective circuit: it is composed of a diode and some resistances. They are bound by a flat cable (34 drivers). Finally the two parts could have been drawn on the same printed circuit. I chose to install the protective circuit close to surface bus since, anyway, I needed to manufacture a box which was going to be used as junction, so I chose to include the resistances and the diode as well.

The diodes are used to avoid a short circuit when several strips connected to the 74hc595 are in contact. The resistances (1 KOhm) connected to the 74hc165 are "pull down": they help eliminate unwanted noise.

The plans of the following printed circuits were designed for a resolution of 16 X 16 contacts.

Circuit imprimé For the manufacture of your printed circuit I propose to you to use the MG Chemical products. You need the kit of exposure, the kit of photomanufacture and the kit of engraving. The steps are very simple and are very well explained on the MG Chemical site. Firstly it is necessary to photocopy the plan of the circuit on an acetate (plastic transparency), then to deposit it on the presensitized copper plate. Then, expose it using a fluorescent light, soak it in the developer, clean with water. Then, plunge the plate in the basin filled with "ferric chloride" oxygenated. Pierce the holes and install the components. Obviously the process is more complex, all must be calculated.

The following files are the plans of the printed circuit, they are usable only by WinBoard of the Ivex company. If it is impossible for you to get this program so that you cannot print the circuit, write to me and I'll be pleased to send the plan under another format (or even directly send the plan to you on transparent paper):

The following diagrams have been put there for mere visual indication. They do not respect the real format of the components. The lines in red indicate where the components and the connections should be placed.

Circuit principal

Cable joint box to be installed close to électrosensitive surface. Resistances have a value of 1 KOhm and the diodes 1n4148.

Boite de jonction

Price of Materials

All prices in canadian dollars. Materials were bought in Montreal.

32 sheets of paperboard
25 X 6 pi of foam
4 aluminium paper rollers
1 sticking paper roller, 4 cm of width
Carpet (to cover the whole)

Stamp Stack
74ch595
74ch165
Flat cable 34 drivers (6 feet)
Copper wire aw22
Connectors with flat cable female and male (34 cond)
Resistances 10 KOhm
Diode
Condenser 47uF
Regulator 7805

Started kit; lamp
Started kit; basin, pump, brush, developer
Printed circuit leaf
Ferric chloride

Total

32 x 0.50 = 16.00$
25 x 2.10 = 52.50$
4 x 11.50 = 46.00$
1.00 $
75.00 $

39.00 $
2.99 $
2.99 $
6 x 1.29 = 7.74$
4.59 $
5.99 $
(package of 100) 6.50 $
(package of 20) 1.99 $
0.99 $
1.99 $

39.00 $
49.00 $
12.99 $
10.45 $

376.71 $

Last Words

It is possible to design the carpet at lower cost. Without forgetting that some of these materials can be recycled. Stamp Stack, as well as the components, can be used for another project. The carpet can be used in your living room !

Finally our project proved very stable and effective. Here are some links which will be surely very practical for you. If you have questions or comments send me an emai: .

For the questions concerning the printed circuits see the MG Chemical website
To find the chips look at the Hvw Tech website
To help you understand the code for the 74CH595/165 see the Parallax website

Credits and Thanks

Design of the electronic interface, text and images: Samuel St-Aubin
Web design and translation: Jean-Sébastien Senécal

The Drone collective is composed of Mathieu Guindon, Julien Keable, Samuel St-Aubin, Jean-Sébastien Senécal and Jonathan Villeneuve.

We would like to thank the BEK center, Gisle Frøysland, Thorolf Thuestad, Roar Stetteland, Hordaland Kunstsenter, Howie, Marie Aboumrad, Mathieu Petit-Clair, the Perte-de-Signal artist-run center and Robin Dupuis.